Windows: New DLL Added to AppInit-DLLs Registry Key

Rule ID

PH_Rule_SIGMA_656

Default Status

Enabled

Description

DLLs that are specified in the AppInit_DLLs value in the Registry key HKLM\Software\Microsoft\Windows NT\CurrentVersion\Windows are loaded by user32.dll into every process that loads user32.dll. This rule is adapted from https://github.com/SigmaHQ/sigma/blob/master/rules/windows/registry/registry_event/registry_event_new_dll_added_to_appinit_dlls_registry_key.yml

Severity

MITRE ATT&CK® Tactics

Persistence

Persistence consists of techniques that adversaries use to keep access to systems across restarts, changed credentials, and other interruptions that could cut off their access. Techniques used for persistence include any access, action, or configuration changes that let them maintain their foothold on systems, such as replacing or hijacking legitimate code or adding startup code.

https://attack.mitre.org/tactics/TA0003

MITRE ATT&CK® Techniques

T1546.010

Event Triggered Execution: AppInit DLLs

Adversaries may establish persistence and/or elevate privileges by executing malicious content triggered by AppInit DLLs loaded into processes. Dynamic-link libraries (DLLs) that are specified in the AppInit_DLLs value in the Registry keys, are loaded by user32.dll into every process that loads user32.dll. In practice this is nearly every program, since user32.dll is a very common library. These values can be abused to obtain elevated privileges by causing a malicious DLL to be loaded and run in the context of separate processes on the computer.

https://attack.mitre.org/techniques/T1546/010

Impacts

Server

Data Source

Windows Sysmon via FortiSIEM Agent

Detection

Correlation

Remediation Guidance

No remediation guidance specified

Time Window

If the following pattern or patterns match an ingested event within the given time window in seconds, trigger an incident.

300 seconds

Trigger Conditions

If the following defined pattern/s occur within a 300 second time window.

Filter

SubPattern Definitions

SubPattern Name: Filter

This is the named definition of the event query, this is important if multiple subpatterns are defined to distinguish them.

SubPattern Query

This is the query logic that matches incoming events

eventType REGEXP "Win-Sysmon-12-Registry-.*|Win-Sysmon-13-Registry-.*|Win-Sysmon-14-Registry-.*" AND (regKeyPath REGEXP "\\SOFTWARE\\Microsoft\\Windows NT\\CurrentVersion\\Windows\\AppInit_Dlls$|\\SOFTWARE\\Wow6432Node\\Microsoft\\Windows NT\\CurrentVersion\\Windows\\AppInit_Dlls$" OR newObjValue REGEXP "\\SOFTWARE\\Microsoft\\Windows NT\\CurrentVersion\\Windows\\AppInit_Dlls$|\\SOFTWARE\\Wow6432Node\\Microsoft\\Windows NT\\CurrentVersion\\Windows\\AppInit_Dlls$") AND (details!="(Empty)")

Group by Attributes

This defines how matching events are aggregated, only events with the same matching attribute values are grouped into one unique incident ID

details,hostName,newObjValue,regKeyPath

Aggregate Constraint

This is most typically a numerical constraint that defines when the rule should trigger an incident

COUNT(*) >= 1

Incident Attribute Mapping

This section defines which fields in matching raw events should be mapped to the incident attributes in the resulting incident.

The available raw event attributes to map are limited to the group by attributes and the aggregate event constraint fields for each subpattern

details = Filter.details,
hostName = Filter.hostName,
newObjValue = Filter.newObjValue,
regKeyPath = Filter.regKeyPath

FortiSIEM Rules